"They were released as planned after some checks," a spokesman for the Belgian federal prosecutor told Reuters. "There were no charges, either."

Four of the men who foiled the train attack were subsequently awarded France's highest honour, the Legion d'honneur. The alleged perpetrator, Ayoub el Khazzani, remains in police custody ahead of his trial on terror charges.

The arrests followed police raids on several properties in Brussels, which saw three men charged for planning a terror attack. Belgian media reports the three planned to attack fans at the Euro 2016 football tournament in France.

No explosives or weapons were found in the raids that resulted in the arrest of the six now released, said police.